Mass reduction in vehicle parts and components lowers the rate of the vehicle's fuel consumption. Thus different materials are considered to form vehicle structure which may be lighter in weight than steel or metal, but yet provide the sufficient structural strength for body support. In particular, it is known to replace metal frames for vehicle components such as seat assemblies with polyurethane, or polypropylene.
Polypropylene has sufficient compression and tensile strength to replace the metal in the manufacture of the seat back assembly flame. Indeed, some vehicle seat backs have done so. Expanded polypropylene (EPP) is generally polypropylene that has been expanded using gas injection during the molding process. EPP has a lower density than polypropylene and thus weighs less than the same volume of polypropylene. Accordingly, it remains desirable to reduce the mass of a seat back assembly by using a frame than is lighter than metal, but yet has sufficient structural integrity so as to withstand the load associated with vehicle operation.
Seat back assemblies contain numerous parts. For instance, a seat back assembly with a pivotable armrest requires a bracket for which the armrest pivots about. The bracket must be further fixed to the seat back assembly. It is known to fix the armrest bracket to the metal frame. This increases production costs as the armrest bracket must be welded to the frame. Further, the armrest bracket must have a planar surface large enough to apply the spot welder to. Thus it remains desirable to have a seat back assembly that requires less mass than that of the prior art seat back assemblies, but yet retains comfort features such as an armrest, headrest, and the like.